Alternans is a risk factor for cardiac arrhythmia, including atrial fibrillation. At the cellular level alternans is observed as beat-to-beat alternations in contraction, action potential (AP) morphology and magnitude of the Ca2 + transient (CaT). It is widely accepted that the bi-directional interplay between membrane voltage and Ca2 + is crucial for the development of alternans, however recently the attention has shifted to instabilities in cellular Ca2 + handling, while the role of AP

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... tion remains poorly understood. This study provides new insights how beat- to-beat alternation in AP morphology affects occurrence of CaT alternans in atrial myocytes.